After you make a post, the "Back to Thread" link doesn't work (it takes you to the topic list instead), but the "Thread" link at the top does.

You can bomb-jump in midair while holding Up and Right, but not while holding Up and Left. (At least, that's how it is on my computer.) You have to let go of one of them before Igor will drop a bomb. Also, your computer might beep at you in a complaining fashion if you hold down too many other keys. Found that out while messing around in 2P mode.

On 23.5, from the button platform, you can triple-jump to the series of ledges closest to the exit portal. Only one saw-dodge required!
In PD62, the rings seem to spawn faster when you clear a level by completing CRISTAL. (Is that true, or was I imagining things?)
On 64.1, if you knock the top lemon down onto the 2x1 platform under its box, it will jump across the 2-square gap to the left and suicide on the spikes.

This is probably already known, but the fruits can appear early on 86 (while the small platforms and black crystal are still invisible) if you bomb-jump high across the room with

.
It's possible to bomb-jump across the gap in 87 if you have at least two bombs or the

at your disposal. A bit quicker and surer than using the red bomb (which seems to spring you up too high and put you back where you started more often than not).

Few things are more enjoyable than strategically using the teleporters against the enemies on 89.
How to say this without undue spoilers? Right, you know that part of the Tuber fight where an arrow appears? It's possible to hit him right in the middle of that sequence. Pretty satisfying.

(I just did it twice in a row by accident.)